a) Ta có: \(\dfrac{\left(5^4-5^3\right)^3}{125^5}=\dfrac{\left[5^3\left(5-1\right)\right]^3}{\left(5^3\right)^5}=\dfrac{5^9.4^3}{5^{15}}=\dfrac{4^3}{5^6}=\dfrac{64}{5^6}\)
b) \(\dfrac{9^3}{\left(3^4-3^3\right)^2}=\dfrac{\left(3^2\right)^3}{\left[3^3\left(3-1\right)\right]^2}=\dfrac{3^6}{3^6.2^2}=\dfrac{1}{4}\)